1. Field of the Invention
The present invention relates to a supporting plate which is attached to a substrate such as a semiconductor wafer to support the substrate when the substrate is thinned, and also relates to a method for stripping the supporting plate.
2. Description of the Prior Art
There has been a need of making IC cards for cell phones thinner, smaller, and lighter. In order to satisfy this need, a semiconductor chip to be incorporated therein must be thin. Although the thickness of a wafer which forms a semiconductor chip is 125–150 μm at present, it is expected that the thickness of a semiconductor wafer must be 25–50 μm for a next generation chip.
A conventional method for thinning a semiconductor wafer is shown in FIG. 7. Specifically, a protecting tape is attached to a surface (A-surface) of a semiconductor wafer on which a circuit (element) has been formed. The wafer is turned over, and the rear surface (B-surface) of the semiconductor wafer is ground by a grinder so as to make the wafer thin. The rear surface of the semiconductor wafer which has been thinned is fixed onto a dicing tape retained by a dicing frame, and the protecting tape covering the surface (A-surface) of the semiconductor wafer on which a circuit (element) has been formed is stripped in this state. Next, the wafer is cut into each chip by a dicing device.
The above-mentioned method has been disclosed in Document 1. According to Document 1, the protecting tape having heat resistance is stripped from the semiconductor wafer by using a strong adhesive tape which is bonded to one end of the protecting tape.
Document 2 has disclosed that a protecting base is obtained by immersing ladder-type silicone oligomer in an aluminum nitride—boron nitride porous sintered material is used instead of a protecting tape, and the protecting base and a semiconductor wafer are bonded by using a thermoplastic film. Document 2 also mentions that they are immersed in pure water at 80° C. for 3 hours before stripping.
Document 3 has disclosed that a protecting base is made of a material having the same thermal expansion coefficient as a semiconductor wafer such as alumina, aluminum nitride, boron nitride, or silicon carbide. Also, Document 3 has proposed a method in which the protecting base and the semiconductor wafer are bonded by using a thermoplastic resin such as polyimide, the semiconductor wafer is thinned by a grinder, and thereafter stripping is performed by immersing in water, amine, or a mixed solution of water and amine, or by using steam.
Although the technical field is different, Document 4 has disclosed that Invar (alloy of 36% Ni and Fe) is used for part of a shadow mask (at the side irradiated with electron beams) for a Braun tube.
[Document 1] Japanese Patent Application Publication No. 2002-270676, paragraph 0035
[Document 2] Japanese Patent Application Publication No. 2002-203821, paragraph 0020
[Document 3] Japanese Patent Application Publication No. 2001-77304, paragraphs 0010, 0017 and 0020
[Document 4] Japanese Patent No. 3440333, paragraph 0007
In the case of using the protecting tape as disclosed in Document 1, cracking or chipping of the semiconductor wafer easily occurs when the tape is stripped. Also, the protecting tape is not sufficient to support the thinned semiconductor wafer. Consequently, transfer needs to be conducted by manpower, and automation is impossible.
In the techniques of Documents 2 and 3, handling or transfer can be automated by using alumina, aluminum nitride, boron nitride, or silicon carbide as a supporting plate instead of a protecting tape. However, since it is difficult for a solvent to enter between the supporting plate and the semiconductor wafer at the time of stripping, it takes too much time to strip the supporting plate from the semiconductor wafer.
Also, the thermoplastic film bonding the support plate and the semiconductor wafer often fails to completely dissolve, and tends to be left in a state of sticking to either one of the support plate and the semiconductor wafer.
Another method has been known in which a glass substrate is used as a supporting plate, the glass substrate and a semiconductor wafer are bonded by using an ultraviolet curable wax or a double-faced adhesive tape, and the glass substrate and the semiconductor wafer are stripped from each other by being irradiated with ultraviolet rays having a different wavelength from the ultraviolet rays used for curing. However, if the circuit-formed surface of the semiconductor wafer is irradiated with the ultraviolet rays, the element (CCD or CMOS) might be damaged.
In the case of using alumina, aluminum nitride, boron nitride, or silicon carbide as the protecting base, since a magnet cannot be employed at the time of stripping, the apparatus must be complicated.